Theoretical study on the excited states and photodissociation mechanism of dimethyldisulfide

The photophysics and photochemistry of dimethyldisulfide (DMDS) provide important clues for the photo-induced reactions between the cysteine residues in proteins. In this Letter, the state-average complete active space self-consistent field (SA-CASSCF) and multi-state extension of multiconfigurational second-order perturbation (MS-CASPT2) approaches are applied to investigate both the vertical excitation energies and the photodissociation mechanism of DMDS. The two lowest singlet excited states are predicted to be pure valence states, while the four higher states apparently have Rydberg characters. In either the S₁ or S₂ state, the S-S fission is the major channel compared with the S-C cleavage.